1. Field of the Invention
The invention relates to a novel class of hydrogen bond complex compounds of formula (I), below, which are useful as intermediates in an improved process for production of benzothiazine carboxamide anti-inflammatory agents.
2. Description of the Prior Art
Two methods for synthesis of N-substituted benzothiazine carboxamide anti-inflammatory agents are disclosed in U.S. Pat. No. 3,591,584. The first of these is used to prepare carboxamides in which the N-substituent is not an heterocyclic moiety. It comprises contacting an organic isocyanate, R.sub.3 NCO, wherein R.sub.3 is, e.g. certain alkyl, phenyl or naphthyl groups, with a 4-oxo (or 3-oxo)1,2-benzothiazine to produce e.g., the compound of the formula ##STR3## or the corresponding 3-oxo-4-carboxamide.
A second method is preferred for the preparation of those amides wherein the N-substituent is an heterocyclic moiety; it involves reaction of the corresponding carboxylic acid ester with the appropriate amine, R.sub.2 NH.sub.2, where R.sub.2 is a heterocyclic group, to produce the desired benzothiazine carboxamide, e.g., ##STR4##
In U.S. Pat. No. 3,891,637 a process is disclosed whereby the N-heterocyclic amides of formula (VII) are obtained from the corresponding N-phenyl amides by a transamidation process.
U.S. Pat. No. 3,853,862 discloses a process for production of 4-oxo-1,2-benzothiazine-3-carboxamides of formula (VII) by cyclization of a benzenesulfonylglycineamide (III) in the presence of a metal hydride, e.g., ##STR5##
U.S. Pat. No. 4,289,879, issued Sept. 15, 1981, discloses a method for preparing piroxicam [4-hydroxy-2-methyl-N-(2-pyridyl)-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide] via the corresponding 3-(2-methoxyethyl) ester.